A microparticle sorting apparatus that forms a microparticle-containing sheath flow in a channel, detects fluorescence and scattered light emitted from the microparticles by irradiating light on the microparticles in the sheath flow, and separates and recovers a microparticle group (population) that exhibits a predetermined optical characteristic is known. For example, in a flow cytometer, a specific type of cell only is separated and recovered by labeling a plurality of types of cell included in a sample with a fluorescent dye and optically identifying the fluorescent dye labeled on each cell.
In Patent Literature 1 and Patent Literature 2, microchip-type microparticle sorting apparatuses are disclosed that perform analysis by forming a sheath flow in a channel formed on a microchip that is made from plastic, glass or the like.
The microparticle sorting apparatus disclosed in Patent Literature 1 controls the feeding direction of the sheath flow at a branching portion between an introduction channel in which the sheath flow is formed and a branch channel in communication with the introduction channel by generating an air bubble based on laser irradiation at the branching portion. According to this microparticle sorting apparatus, controlling the feeding direction of the sheath flow at the branching portion with an air bubble enables just the target microparticles to be collected into the branch channel from the introduction channel and sorted.
Further, the microfluidic system disclosed in Patent Literature 2 sorts target microparticles by using an actuator to control the feeding direction of a sheath flow at a channel branching portion. In this microfluidic system, the actuator changes the feeding direction of the sheath flow by pressing against a chamber that is connected to a branching portion between an introduction channel in which the sheath flow is formed and a branch channel in communication with the introduction channel to push out fluid in the chamber.